I can t count, how to calculate, why the calculated number is wrong...

There are at least 2 balls in the corresponding box, and there are three cases, namely:

1) There are just 2 balls into the corresponding box, then you should pick out 2 balls first, there are c(5,2) methods, and then put the remaining 3 balls in, because these 3 balls can not be put in pairs, so there are only two ways to put it, then there are a total of c(5,2) 2 ways in this case;

2) There are just 3 balls into the corresponding box, then in the same way, first select 3 balls, there are c(5,3) methods, and then put the remaining 2 balls in, can not be put in the number, so there is only 1 way to put it, in this case there are a total of c(5,2) methods;

3) All 5 balls should be placed (there is no case where 4 balls should be placed accordingly);

Then, the three situations add up to the total way to put it.

c(5,2) 2+c(5,3)+1=20+10+1=31 species.

Solution: According to the meaning of the topic, the tree diagram shows that there are 5*4*3*2*1=120 kinds of results.

The result of at least 2 balls in the corresponding box is 3*3*2*1=180.

c(5,2)*2+c(5,3)+1=31

If there are exactly two balls, the same situation is c(5,2)*2

There are exactly three balls in the same case as c(5,3).

There are exactly five balls and the same situation is 1

double p,w,s,d,f;

printf("Please enter the freight P, the weight of the goods W, the transportation distance S:");

It should be scanf("%lf%lf%lf",&p,&w,&s);

if(s<250) d=;

else if(s<500) d=;

else if(s<1000) d=;

else if(s<2000) d=;

else if(s<3000) d=;

else d=;

f=p*w*s*(;

printf("The total shipping cost is %f",f);

Each paragraph should be counted separately. For example, s=900, then f=250+250*(; ok？

Unless your keys are broken.

Because you didn't press 0, so if you press 0 more, it's useless, in fact, it's 2 1, so it's 2

I think there may be a messy writing on your manuscript paper, so I suggest that you divide the manuscript paper into blocks with a ruler, and use the manuscript paper to be as organized as writing homework (this does not delay much time), so that you will not have to check it after you have finished writing. You can also circle the answers with different colors (red pen) ratios, and then pair them after copying. If you are nervous in the exam room, you will draw the wrong card, there are only 12 choices in high school mathematics, after the choice and fill in the blanks are done, paint the card, write the answer on the card on the manuscript paper after drawing the card, and check it with the previous one, it will only take about a minute, you can avoid this low-level error.

Relax your mind, concentrate, don't be too nervous, you can learn some ways to face the college entrance examination correctly, and avoid some mistakes in the previous college entrance examination in education.

I used to do the same, but then I did more, and I did it faster and faster, and I typed the draft neatly, checked one test paper three times, and didn't use the old habitual thinking to do it when checking, and then I became thoughtful.

Excuse me, if you don't withdraw money on the day of regular maturity, there is still current interest.

The height is the root number 401 48, and the area is 12 * the root number 401 48

Strange?? What do I think of you, this is an acute triangle??? What is an obtuse angle...

There is a formula to find the size of an angle according to the cosine theorem, and then according to s=absinc 2, it is estimated that I have not learned it in the second year of junior high school.

s=sqrt[p(p-a)(p-b)(p-c)];p= sqrt stands for open square root.

According to the above equation p=

s=sqrt[p(p-a)(p-b)(p-c)]=sqrt[